New Zealand: Adverse weather forecast across southern and western South Island through at least Aug. 13

Event

Heavy rainfall, strong winds, and possible flooding are forecast to occur across southern and western South Island, New Zealand, through at least Aug. 13. The affected areas include western Canterbury, Otago, Southland, northern Tasman, and West Coast regions. The New Zealand National Meteorological Service has issued the following heavy rainfall and strong wind watches and warnings across the affected area:

• Heavy Rain Warning: The ranges of Westland, south of Otira; Fiordland; the headwaters of the Canterbury lakes and rivers, south of Arthur's Pass; 7-13 cm (3-5 inches) of rain is possible.

• Strong Wind Warnings: Canterbury High Country; Southern Lakes; Central Otago; Clutha; inland Dunedin; Fiordland; Southland; Stewart Island; strong winds of up to 120 kph (75 mph) are possible.

• Heavy Rain Watch: The ranges of Buller and Westland, from Otira northwards; the headwaters of the Otago lakes and rivers; the ranges of Nelson west of Motueka.

Authorities will likely issue new alerts or update/rescind existing advisories as weather conditions change over the coming days.

Hazardous Conditions
The storms could produce rounds of heavy rainfall, strong winds, and isolated thunderstorm activity across southern and western South Island. Sustained heavy rainfall could trigger flooding in low-lying communities near rivers, streams, and creeks. Urban flooding is also possible in developed areas with easily overwhelmed or a lack of stormwater drainage systems. Sites located downstream from large reservoirs or rivers may be subject to flash flooding after relatively short periods of intense rainfall. Landslides are possible in hilly or mountainous areas, especially where the soil has become saturated by heavy rainfall. Power outages could occur throughout the affected area.

Transport
Floodwaters and debris flows may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around the affected areas. Ponding on road surfaces could cause hazardous driving conditions on regional highways. Authorities could temporarily close some low-lying routes that become inundated by floodwaters. The disruptive weather may cause some delays and cancellations at regional airports. Authorities may temporarily suspend port operations along the Tasman Sea, South Pacific Ocean, and Foveaux Strait if strong winds trigger hazardous sea conditions, impacting freight and passenger maritime traffic. Flooding could block regional rail lines; freight and passenger train delays and cancellations are possible in areas that see heavy rainfall and potential track blockages.

Disruptions triggered by inclement weather and resultant hazards, such as flooding, could persist well after conditions have improved - it could take days before any floodwaters recede and/or officials clear debris. If there is severe damage to infrastructure, repair or reconstruction efforts may result in residual disruptions.

Advice

Monitor local media for weather updates and related advisories. Confirm all transport reservations and business appointments before travel. Make allowances for localized travel delays and potential supply chain disruptions where flooding has been forecast. Do not drive on flooded roads. Charge battery-powered devices in the case of prolonged electricity outages.

Resources

New Zealand National Meteorological Service